Faolyn
(she/her)
Well, why not? Lots of games do racial templates you can alter just by paying a different cost, or say that race has no mechanical effect. And quite frankly, since so many species have darkvision in D&D, there's almost no point in caring about lighting in the first place--might as well say that either nobody has darkvision (which I believe Shadowdark does) or everyone can see in the dark.Ok, but certainly the same logic applies to all the species traits then? Like if I want to have halfling that was raised in Underdark and has adapted to have dark vision, why cannot I have that? If every PC is an unique exceptional individual that doesn't need to conform what is normally possible to their species, then why the hell we even have dedicated rules splats for the species? Why not just have a bunch of traits and bonuses people can choose and can fluff however they wish?
But even in D&D, maybe a halfling could become exposed to Underdark radiation and gain darkvision. Or used a special concoction unknown to surface folks to obtain darkvision. Level Up does that with a couple of their Cultures--if you take the Deep Gnome, Deep Dwarf, or Shadow Elf cultures, you get darkvision. After all, "realistically," a subterranean people would just go blind and develop good hearing and smell, or tremorsense, or something like that, meaning that darkvision, especially the enhanced darkvision of many Underdark races, could be due to magical radiation or alchemical concoctions.
Just make the player give up another trait of equal value--which is no different than, if you're using point buy, deciding that putting that 15 in Strength means that you won't have as high a Dex or Int or whatever. "You can pick Darkvision but to balance things out, you won't have the Nimbleness trait. Because the part of your brain that was being used for that level of agility has been repurposed for enhanced vision."